According to Merry, the prototype of a great strategist is Mr. Nosey - a fictitious character, who is always snooping around in other people's lives. As a planner, you have to be endlessly curious, maybe to the point where other people think you're weird. Going shopping? Don't forget to check out other people's shopping carts and follow them around, analyzing their shopping and buying preferences. Insights are everywhere, you just have to look for them.
Besides being curious, a good planner must have great listening skills, and empathy lies at their core. You have to be able be "put yourself in your consumer's shoes." And then walk in them. Only this way you can truly understand this person's feelings and experiences, which is the foundation for any great strategy. In fact, a good planner should know (despite what the client may say) that brands belong to consumers, not brand owners, so understanding your consumer is key here.
Most strategies can be divided into two categories: rational and emotional. It would be intuitive to say that a strategy must be rational, but it turns out that those advertising campaigns that utilize emotional strategies are more successful on average. People are highly emotional and most of the time irrational in their actions. Think about this: when shopping, you fall in love with a beautiful pair of shoes. Do you weigh all the pros and cons BEFORE you buy it or do you post-rationalize your purchase AFTER you buy it? Most people do the second, which proves that we are more emotional than rational, and as strategists, we should be aware of that. "It's all about an emotional response," as Merry puts it.
One more interesting thing that Merry suggested everyone should do is take the Myers-Briggs personality test, like this one here. Self-awareness is very important in this business (actually, in any). The better you understand yourself, the better you know how to build stronger relationships with people, the better you know how to deal with problems. According to the test, I am the ISTJ type (Introverted, Sensing, Thinking, Judging), aka "the duty fulfiller" or "the inspector." Can't but agree with that. While I'm figuring out my strengths and weaknesses, take this test to learn more about yourself! (You can read about each personality type here and here).